Conventionally, aluminum (Al) and aluminum alloy has been typically used as a wiring material for semiconductor device manufacture. Besides, copper (Cu) is being studied for use as a wiring material because of its low resistance. These films are formed with sputtering method or chemical vapor deposition (CVD) method, and basically the wiring formed with these methods has a polycrystal structure.
If a large amount of electric current flows through this polycrystal-structured wiring for a long time in response to an action of an IC, momentum of electrons is given to atoms of the wiring material (e.g., aluminum atoms), and therefore the atoms are moved. These phenomena are called electromigration. After the atoms are moved, a void occurs in the wiring, and, in an extreme case, the wiring is cut off.
If an external tensile stress is applied to the polycrystal-structured wiring, the atoms of the wiring material (e.g., aluminum atoms) are moved in the same manner as above, which causes, for example, a void to occur in the wiring and the wiring to be cut off. These phenomena are called stress migration. All the phenomena described so far are known to occur in a crystal grain boundary where activation energy is the lowest to move the polycrystal-structured wiring material. For example, in the aluminum wiring, the phenomena are known to occur in a crystal grain boundary where activation energy is 0.5 eV. For example, in a case of the aluminum wiring, 0.2 to a few % of impurity such as copper, palladium and/or titanium are/is mixed to restrain dispersion of the aluminum in that crystal grain boundary.
However, this is still not capable enough to cope with an increasing electric current density in high speed devices of submicron rule. Therefore, more reliable wiring is in demand.
With such a demand in scope, monocrystallization of wiring of, for example, aluminum has been attempted lately. If monocrystallization completely eliminates the crystal grain boundary, a higher activation energy is required for the movement causing the electromigration and stress migration phenomena, thereby improving reliability of the wiring. For example, in a case of aluminum, the monocrystallization almost triples the activation energy required for the movement, up to about 1.4 eV.
However, it is very difficult to conduct such monocrystallization with an entire wafer surface. A monocrystallization method currently in study is disclosed in Japanese Laid-Open Patent Application No. 4-44229/1992 (Tokukaihei 4-44229). According to the method, first, aluminum formed with sputtering method on a barrier metal receives patterning and is coated with a plasma SiO.sub.2 film. Then, the plasma SiO.sub.2 film on the aluminum is removed with etchback to expose the aluminum. Next, high speed heating treatment is carried out with an infrared ray lamp, carbon strip heater or the like to instantly melt the aluminum at 500 to 600.degree. C. for 10 to 30 seconds. Finally, the aluminum is gradually cooled so as to be monocrystallized with solid phase epitaxial growth method.
Meanwhile, according to a method disclosed in Japanese Laid-Open Patent Application No. 4-247625/1992 (Tokukaihei 4-247625), a polycrystal aluminum film having a thickness of 0.05 to 0.2 .mu.m is formed with heating treatment using DMAH ((CH.sub.3).sub.2 AlH) as a material or with plasma CVD method on a silicon oxide film whose monocrystal silicon is partly exposed. As a result, a monocrystal aluminum film grows on the monocrystal silicon. Then, the polycrystal aluminum film is annealed at 500 to 600.degree. C. Consequently, the polycrystal aluminum film is monocrystallized with the monocrystal aluminum film as a core. A monocrystal aluminum film is thus formed on the entire wafer surface.
Nevertheless, in the method disclosed in Japanese Laid-Open Patent Application No. 4-44229/1992, it would be difficult to form uniform monocrystal on the entire wafer surface with no seed crystal. Therefore, although gradual cooling alone could form aluminum crystal of a big grain diameter, the crystal formed in such a manner would have a polycrystal structure.
Moreover, according to the method disclosed in Japanese Laid-Open Patent Application No. 4-247625/1992, a silicon substrate is used as a seed crystal to monocrystallize the aluminum thereon. Therefor, the method needs the monocrystal silicon serving as the seed in the bed. Consequently, the method can not be widely applied. Specifically, for example, monocrystallization can not be carried out in second and third layers of multilayer wiring. Besides, if temperature varies on the wafer surface, or if there is an area on the wafer surface where heat radiation is locally inconsistent, it becomes very difficult to control the speed of gradual cooling and the temperature in the wafer surface. It is thus difficult to carry out monocrystallization on the entire wafer surface.